Looks like Bioshock Infinite might not include a multiplayer mode based on the reaction of including it in Bioshock 2 and lack of people playing online weeks after the game was released. If the game does get multiplayer, its only going to be done once the single player is done instead of splitting the team up to do both at the same time like Bioshock 2.
http://kotaku.com/5617852/multiplaye...shock-infinite